Structure organization of sexithiophene vapour deposited onto HOPG and SiH/Si(111)

We have studied the morphology and structure of thin films of sexithiophene (6T), vacuum deposited onto Highly Oriented Pyrolytic Graphite (HOPG) and SiH/Si(111) substrates, using UV-Vis and Infrared absorption spectroscopy, Transmission Elecron Microscopy and Electron Diffraction. The evaporated films on HOPG show a monocrystalline structure, which is retained even over several hundred Angstroms thickness (1000 Å). On SiH/Si(111) evaporated films have a different structure from the bulk. This latter is lost for thicknesses larger than 500–1000 Å, owing to the generation of high densities of defects which leads to an apparently random polycrystalline film.